There are many different types of Light Emitting Diode (LED) assemblies. FIG. 1 (Prior Art) is a top-down diagram of one such LED assembly 1. LED assembly 1 includes four laterally-contacted LED dices 2-5 that are mounted on a metal core substrate 6. Substrate 6 in this case is a Metal Core Printed Circuit Board (MCPCB). Areas 7-10 illustrated in dashed lines represent portions of a metal layer that is disposed underneath a solder mask layer 11 (see FIG. 2). Reference numeral 12 identifies a portion of metal portion 7 that is exposed through a first opening in the solder mask layer 11. Similarly, reference numeral 13 identifies a portion of metal portion 8 that is exposed through a second opening in solder mask layer 11. These exposed portions 12 and 13 serve as bond pads. Ring structure 14 is a retaining ring of silicone. An amount of a material often referred to as phosphor 15 is disposed within the ring structure 14 over the LED dice. This phosphor actually comprises silicone and particles of phosphor that area embedded in the silicone.
FIG. 2 (Prior Art) is a simplified cross-sectional diagram of LED assembly 1 of FIG. 1. MCPCB 6 includes an aluminum layer 16, a global dielectric layer 17, a layer 18 of metallization of which metal portions 7-10 are parts, and solder mask layer 11. Layer 18 of metal may involve multiple sublayers of metal including an upper layer of a very reflective metal such as silver. Metal portion 10 is a square pad of metal upon which the LED dice 2-5 are mounted. The LED dice 2-5 are fixed to pad 10 by associated amounts of silver epoxy. Amount 19 of silver epoxy is shown fixing LED die 4 to pad 10. Amount 20 of silver epoxy is shown fixing LED die 5 of pad 10. Reference numerals 21-23 identify wire bonds.
A layer 24 of a Highly Reflective (HR) material is disposed within ring 14 between and around the dice 2-5 and wire bonds 21-23 as illustrated. The diagram is simplified in that the regions of the HR material have smooth and rounded edges. Some of the light emitted by LED dice 2-5 may be absorbed by phosphor particles in phosphor 15. These particles may then fluoresce and re-emit light such that this light is directed downward, rather than upward as is desired. Reference numeral 35 identifies one such particle of phosphor. A light ray 36 is emitted from the top of LED die 4 and travels up and is absorbed by particle 35. A second light ray 37 is then emitted from particle 35 and this second light ray travels back downward as shown. HR material 24 is provided so that this light ray will be reflected so that it can pass upward and out of the assembly as light ray 38. Particle 35 is but one such particle. There are numerous particles dispersed throughout the silicone material of phosphor 15. Light emitted from the LED dice 2-5 can be emitted in various different directions including out of the sides of the LED dice. Similarly, a light ray emitted from a phosphor particle can travel away from the particle any direction. The illustration of particle 35, of the direction of light emission from particle 35, and of the associated light rays 36, 37 and 38 in FIG. 2 are only representative of one such particle and its associated light rays. An example of an HR material is a silicone material that is commercially available from ShinEtsu Chemical Co. Ltd. of Tokyo, Japan.
FIGS. 3-10 (Prior Art) illustrate a prior art method of manufacturing the LED assembly 1 of FIG. 1. FIG. 3 (Prior Art) is a top-down diagram of a panel 25 of MCPCBs. MCPCB 6 is one of the MCPCBs of the panel. FIG. 4 (Prior Art) is a top-down diagram of the pad portion 10 of the MCPCB portion 6 of panel 25. This pad portion 10 is exposed through an opening in the solder mask layer 11. FIG. 5 (Prior Art) is an illustration of a screen printing mask 26 used in the next step of forming the layer 24 of Highly Reflective (HR) material. FIG. 6 (Prior Art) is a diagram that shows the result of using the screen printing mask 26 of FIG. 5 to deposit the HR layer 24 onto panel 25. HR material of layer 24 is deposited in the shaded circular region. This circular region is in the center of MCPCB 6. As illustrated, there are eight windows 27-34 in the circular HR layer 24. FIG. 7 (Prior Art) is a diagram that shows the result of a next die attach step. Each of the four dice 2-5 is attached by an amount of silver epoxy in a corresponding one of the four center windows 27-30 in the HR layer 24. Each of the openings 27-30 in the HR layer is slightly larger than its associated die in order to accommodate variations in physical dimensions and inaccuracies of the placement of the dice and wire bonds. FIG. 8 (Prior Art) is a diagram that shows the result of a next step of attaching wire bonds. Only three of the wire bonds 21-23 are identified in the diagram with reference numerals. Some of the wire bonds extend between dice. Others of the wire bonds extend from a die to a conductive upper layer of the substrate. FIG. 9 (Prior Art) shows the result of a next step of forming retaining ring 14. Retaining ring 14 is formed so that it encircles the circular layer 24 of HR material as illustrated. FIG. 10 (Prior Art) shows the result of a next step of placing the phosphor 15 over the LED dice 2-5 in the area bounded by retaining ring 14. After the phosphor 15 has cured, the panel 25 is singulated to form multiple LED assemblies of which LED assembly 1 is one.